Abstract

Auditory evoked potential (AEP) data are commonly obtained in air while sea lions are under gas anesthesia; a procedure that precludes the measurement of underwater hearing sensitivity. This is a substantial limitation considering the importance of underwater hearing data in designing criteria aimed at mitigating the effects of anthropogenic noise exposure. To determine if some aspects of underwater hearing sensitivity can be predicted using rapid aerial AEP methods, this study measured underwater psychophysical thresholds for a young male California sea lion (Zalophus californianus) for which previously published aerial AEP thresholds exist. Underwater thresholds were measured in an aboveground pool at frequencies between 1 and 38 kHz. The underwater audiogram was very similar to those previously published for California sea lions, suggesting that the current and previously obtained psychophysical data are representative for this species. The psychophysical and previously measured AEP audiograms were most similar in terms of high-frequency hearing limit (HFHL), although the underwater HFHL was sharper and occurred at a higher frequency. Aerial AEP methods are useful for predicting reductions in the HFHL that are potentially independent of the testing medium, such as those due to age-related sensorineural hearing loss.

Received 02 September 2011Revised 17 February 2012Accepted 27 February 2012Published online 04 May 2012

Acknowledgments:

The authors would like to thank Kari Wickersham, Amber Arnold, Jen Sabo, and Lisa Gibler for their assistance in training the subject. Carolyn Schlundt and Jennifer Trickey assisted in data collection. Whitlow Au provided the J-9 transducer. This work was funded by the SSC Pacific In-House Laboratory, Independent Research Program and the US Office of Naval Research, Marine Mammals and Biological Oceanography Program.